What is the middle cut in distilling?

The distillate from the spirit still is separated into three parts: the head or foreshots, the heart or middle cut, and the tail or feints.

The Glasgow Distillery describes that the distillate is split into these three parts as it comes off the still, and that the distiller goes by time, appearance, smell and taste to do so. Only the middle part goes to the receiving tank as new make spirit, and that is the part that is later filled into casks. In English that heart is also called the heart or spirit cut; in Dutch people speak of the heart of the run.

Common cut strengths are around 72 percent alcohol at the start and 63 percent at the end, but every distillery chooses this for itself.

The Glasgow Distillery cites a cut from 72 to 63 percent alcohol for its unpeated, double-distilled whisky and a cut-off at 57 percent for the peated variant. Waterford Distillery takes the heart off at around 66 percent alcohol. Whisky Magazine cites an average spirit cut of about 70 percent. Those are common margins in practice and not legal limits: the Scotch Whisky Regulations 2009 only stipulate that Scotch is distilled at less than 94.8 percent alcohol, so that the distillate retains the aroma and flavour of the raw materials.

The spirit safe is the instrument with which the cut is made: a closed cabinet of copper and glass in which the distiller sees the distillate run and measures the strength.

According to Whiskipedia, the British Excise Act of 1823 requires anyone who distils whisky legally to install a spirit safe. The cabinet was originally secured with a padlock whose key the customs kept, so that the quantities could be tracked for excise duty. All parts can be operated from the outside with levers, so contact with the distillate is not necessary. Waterford describes the spirit safe as the place where the first distillate becomes visible and where the course of the run is followed.

The foreshots and feints are combined and redistilled with the next charge of low wines, so no alcohol is lost in the distillery.

The Glasgow Distillery calls this a continuous loop: the heads and the tails of one run are added to the next distillation of low wines. Whisky Magazine describes the same and writes that foreshots and feints are collected to be distilled again with the next charge of low wines. Waterford sends the heads to the low wines tank instead of to the final product.

Where the distiller switches the heart on and off again determines which aroma compounds end up in the new distillate, and a wider cut takes along more compounds from the tails.

Whisky Magazine writes that the point at which collection starts and stops determines the aroma range, and that fruity esters are found mainly at the start of the run, in the range of 72 to 68 percent alcohol. Waterford points out that as the alcohol percentage falls, certain fusel oils begin to appear in the distillate, and therefore makes a narrow cut by aroma and taste rather than by the clock. That distillery puts purity above yield.

In the bottle you see the cut mainly in the strength, because Scotch generally goes into the cask at 63.5 percent alcohol and is bottled at at least 40 percent.

The Scotch Whisky Association cites 63.5 percent alcohol as the usual filling strength for the cask, and the Scotch Whisky Regulations 2009 prescribe a minimum of 40 percent alcohol when bottling. In Bathmen there are 2,016 bottles of Scotch whisky of 46 percent or more, from 248 brands, with alcohol percentages from 46 to 66.8 percent. The whole whisky shelf has 3,898 items, of which 2,783 are from Scotland. The largest brands in that selection are Adelphi with 70 bottles, Signatory with 62, Glenallachie with 59 and Kilchoman with 58.